Gesture Recognition Questions

• Question: What are the disadvantages of deleting the first point at a particular location?
• Loses acceleration (and speed) to that point (removed first time stamp)

• What are the disadvantages of deleting the second point at a particular location?
• Loses acceleration (and speed) from that point onwards (removed second time stamp)

• Question: What are the disadvantages and advantages to removing the first point when there are duplicate time stamps?
• If it is assumed that the duplication of time stamps is the result of a very quick motion and we call 4 consecutive points a,b,c and d where timestamp(b)=timestamp(c)Then discarding point b will result in less digitization noise for the change of angle between a and c but more noise between c and d. Since the farther two points are, the less noisy is the angle between them.

• What are the disadvantages and advantages of removing the second point?
• Same as above, but here the advantage is less noise between b and d but more noise between a and b.

• What are the disadvantages and advantages of altering the time stamp values?
• If we alter the time stamps then we will not lose any of the points thus no data is discarded. However in order to differentiate between the two points, their time stamp has to be an epsilon seconds apart. Epsilon has to be smaller than the maximum timer resolution. The disadvantage of altering the time stamps is that if the two consecutive points have noise in their spatial location, small epsilon values will amplify that noise in the speed measurements

• What would be the best way to do this?
• We can take the mean of the duplicate points and regard it as the sole point with that timestamp with the assumption that the sampling rate is uniform. This way, no data is discarded but might need more computation.

• The Rubine features were calculated for the shapes below. Can you match up the shape letter label from Figure 10 with their Rubine features in Figure 11?
• Answers were in the document

• Questions: What was the insight behind the other features that Long used?
• Total angle traversed / total length: some how an average curvature. Circles of different sizes will differ in this measure
• Density metric 1: a lengthy stroke which ends near its starting point probably has all of its point in a small neighborhood around the starting point which makes it dense. However there are cases that this does not apply
• Density metric 2: The rationale is similar to the previous but unlike that, it doesn't rely on the distance of only the first and last points, but somehow takes into account the whole stroke
• Opnness: closed curves will result in lower value for this measure while a straight line would result in larger values
• Area of bounding box: a measure of size of the stroke. However sensitive to rotation and error prone
• Log(area): to compensate for large area differences in larger shapes while the difference in perception is not as high
• Total angle / total absolute angle: Some how measures how much the stroke changes its rotation direction, the lower times it changes, the higher this measure will be